This invention is directed to compounds which inhibit the RNA-dependent RNA polymerase (RdRp) encoded by Hepatitis C virus (HCV). The compounds, or pharmaceutically acceptable salts thereof, are useful for the treatment of HCV viral infections.
HCV is a major human pathogen, infecting an estimated 170 million people worldwide. A substantial fraction of these HCV infected individuals develop serious progressive liver disease, including cirrhosis and hepatocellular carcinoma. (Lauer, G. M.; Walker, B. D. N. Engl. J. Med. (2001), 345, 41–52).
Presently, the most effective HCV therapy employs a combination of alpha-interferon and ribavirin, leading to sustained efficacy in 40% of patients. (Poynard, T. et al. Lancet (1998), 352, 1426–1432). Recent clinical results demonstrate that pegylated alpha-interferon is superior to unmodified alpha-interferon as monotherapy (Zeuzem, S. et al. N. Engl. J. Med. (2000), 343, 1666–1672). However, even with experimental therapeutic regimens involving combinations of pegylated alpha-interferon and ribavirin, a substantial fraction of patients do not have a sustained reduction in viral load. In addition, the prospects for development of a prophylactic or therapeutic vaccine appear dim, in spite of intensive research efforts. Thus, there is a clear need to develop effective therapeutics for treatment of HCV infection.
HCV is a positive-stranded RNA virus. Based on comparison of deduced amino acid sequence and the extensive similarity in the 5′ untranslated region, HCV has been classified as a separate genus in the Flaviviridae family. All members of the Flaviviridae family have enveloped virions that contain a positive stranded RNA genome encoding all known virus-specific proteins via translation of a single, uninterrupted, open reading frame.
Considerable heterogeneity is found within the nucleotide and encoded amino acid sequence throughout the HCV genome. At least six major genotypes have been characterized, and more than 50 subtypes have been described. The major genotypes of HCV differ in their distribution worldwide, and the clinical significance of the genetic heterogeneity of HCV remains elusive despite numerous studies of the possible effect of genotypes on pathogenesis and therapy.
The RNA genome is about 9.6 Kb in length, and encodes a single polypeptide of about 3000 amino acids. The 5′ untranslated region contains an internal ribosome entry site (IRES), which directs cellular ribosomes to the correct AUG for initiation of translation. The translated product contains the following proteins: core-E1-E2-p7-NS2-NS3-NS4A-NS4B-NS5A-NS5B. This precursor protein is cotranslationally and posttranslationally processed into at least 10 viral structural (core, E1, E2) and nonstructural (NS2-NS5B) proteins by the action of host cell signal peptidase and by two distinct viral proteinase activities (NS2/3 and NS3).
Although the functions of the NS proteins are not completely defined, it is known that NS3 is a serine protease/RNA helicase, NS4A is a protease cofactor, and NS5B is an RNA dependent RNA polymerase involved in viral replication. It has recently been demonstrated that functional NS5B is required for virus infectivity in chimpanzees (Kolykhalov, A. A. et al. J. Virol. (2000), 74, 2046–2051). Because HCV only infects chimpanzees and humans, this result strongly suggests that inhibition of the NS5B RdRp is a viable approach for the development of HCV therapeutic agents.